Combustion chamber for gas turbines and the like having a fluidized burner bed

ABSTRACT

A combustion chamber with a fluidised burner bed, preferably for gas turbines, comprising means for controlling the supply of fuel, combustion air and a cooling medium for the fluidised bed to maintain a predetermined proportional relationship therebetween constant under varying load conditions.

United States Patent [191 Harboe Dec. 9, 1975 COMBUSTION CHAMBER FOR GASTURBINES AND THE LIKE HAVING A FLUIDIZED BURNER BED [75 Inventor: HenrikHarboe, Kingston, England [73] Assignee: Stal-Laval Turbin AB, Finspong,

Sweden 221 Filed: July 2,1973

21 Appl. No.: 375,781

[30] Foreign Application Priority Data July 7, 1972 Sweden 8983/72 [52]US. Cl. 60/39.18 C; 122/4 D [51] Int. Cl. FOZC l/00 [58] Field of Search60/3918 C, 39.05, 39.46; 1-22/4 D; 23/288 S [56] References Cited UNITEDSTATES PATENTS 2,482,791 9/1949 Nettel et al. 60/3918 C 2,842,102 7/1958Blaskowski 122/4 D 3,446,012 5/1969 Foster-Pegg 60/39.46 3,687,1158/1972 Bell 122/4 D Primary ExaminerC. J. Husar Assistant Examiner-O. T.Sessions Attorney, Agent, or Firm-Eric Y. Munson [57] ABSTRACT Acombustion chamber with a fluidised burner bed, preferably for gasturbines, comprising means for controlling the supply of fuel,combustion air and a cooling medium for the fluidised bed to maintain apredetermined proportional relationship therebetween constant undervarying load conditions.

9 Claims, 1 Drawing Figure US. Patent Dec. 9 1975 Confro/ meansCOMBUSTION CHAMBER FOR GAS TURBINES AND THE LIKE HAVING A FLUIDIZEDBURNER BED BACKGROUND OF THE INVENTION In the operation of gas turbines,for example, there has been a frequent demand for any kind of fuelsincluding particulate solid fuel. However, so far, the latter has onlyreached an experimental stage owing to the difficulties associated witheffective purging of the combustion gases. The ashes whirled up orfluidized in and accompanying the combustion gases have caused erosionas well as deposits on the turbine vanes, which,

seems to be due among other things to the fact that the combustiontemperature in burners heretofore used is so high that the ashes meltand thus acquire a glazed character and a consequently high grindingcapacity. Therefore, it has been proposed recently to use combustionchambers with a fluidised bed burner combined with a cooling system.

Combustion chambers with a fluidised bed burner, in which the combustiontakes place in a bed of solid cominute or granulated material, which isfluidised in air, produce an advantageously efficient combustion at amoderate temperature and with a moderate amount of excess air.Consequently the ash is not melted down but retains a substantially softconsistency.

Furthermore, this combustion chamber is capable of burning gaseous andliquid full as well as particulate, solid fuel. A disadvantage resultsfrom the difficulty of controlling the combustion under varying loadconditions. One possibility of controlling the combustion is to dividethe chamber into sections which can be selectively connected anddisconnected as shown, for example, in US. Pat. No. 2,842,102. However,this arrangement results in a discontinuous control. Another possibilityis to vary the depth of the fluidised bed so that the bed material iseither discharged or recharged with consequent complications.

Another problem is the cooling which is normally effected partly bywater and partly by steam, the combustion chamber thus operating as aboiler. This normally means that water in the cooling system must bedrained off or blown out when the combustion chamber is temporarilyinactivated, so that the fluidised bed will be able to maintain itstemperature until reactivated 700950C. Within this temperature rangethere is no I melting of the ash which therefore is retained as a soft,

amorphous powder with a low erosion capacity and a low tendency tobecome sticky and to form deposits.

The cooling air and the combustion gases can be mixed after theirpassage through the combustion whereupon the cooling system must berecharged. For

this reason, this type of combustion chamber is impractical forintermittent operation.

SUMMARY OF THE INVENTION The present invention eliminates thesedisadvantages and makes it possible to operate a fluidisationcombustionchamber having a fluidized burner bed of constant temperature and beddepth, while still achieving a high degree of control of the combustionwithin wide limits and permitting intermittent operation.

The important feature of the combustion chamber according to theinvention resides in the fact that its cooling system works with air orsome other gaseous medium that a predetermined relation is constantlymaintained between the amounts of combustion air and cooling air. THeamount of fuel is thus adjusted to the amount of combustion air undervarying load conditions.

The invention contemplates the maintenance of a predetermined proportionbetween combustion air and chamber and be supplied, for example, to agas turbine as a single stream. Another possibility is to keep the twoair streams separated and conduct each of them separately to itsrespective gas turbine, and in this manner the stream of cooling airwith its turbine can then be maintained as a purged system. Thecombustion gases must be separated from ashes and fluidized particlesfrom the burner bed in a dust separator, for example a cyclone, but asmentioned above the combustion gases constitute a minor part of thetotal air current.

BRIEF DESCRIPTION OF THE DRAWING:

The invention will be further explained with reference to theaccompanying drawing which illustrates diagrammatically a combustionchamber embodying the invention.

DESCRIPTION OF A PREFERRED AND A MODIFIED EMBODIMENT From a compressoror an air storage (not shown) the air enters the conduit 1 through thecontrol valve 2. If the air should come directly from a compressor, itmay be advantageous to supplement the valve 2 with a damper (not shown)the passage from the compressor. The air is passed to a space 3 betweenan outer and inner turbine casing and from there into the outer casing 4where the air is divided into combustion air and cooling air.

In the lower part of the casing 4 the combustion air is passed throughadjustable dampers or valves 5 into the bottom of the proper combustionchamber 6. Here the air passes up through a perforated bottom 8 and intothe fluidised bed 9 consisting of a particulate, solid material which iswhirled up in the form of a suspended fluidised bed by the combustionair flowing therethrough. A fuel pipe 7 with a fuel dispenser head atthe upper end supplies said fluidised bed, with the fuel and possiblyalso with new bed material.

As mentioned herein, the fuel may be gaseous or liquid, but also solid,crushed fuel is feasible. The fluidised bed has the advantage of beingcapable of burning a somewhat more coarse-grained fuel than that used inburners for pulverized coal such as boilers. By a suitable choice of bedmaterial, it is also possible to obtain a considerable absorption ofadventitious substances in the fuel. For example bed material containinglimestone is capable of absorbing sulphurous compounds in the fuel, andin this case the sulphur-saturated bed material must be discharged fromthe upper part of the bed and new material be added to the lower part.

From the bed 9 the flue-gas passes up through the dust separator,suitably cyclone separators 10 with exhaust pipes 18 in the bottom,through which ash and whirled-up bed material are separated. From theseparators the purified gas is passed out into the space 11 between theinner combustion chamber 6 and the intermediate casing 19, from wherethe flue-gas passes through the pipe 12 to the gas turbine 20.

The cooling air rises from the bottom of the outer casing 4 through thespace 13 between the outer casing 4 and the intermediate casing 15 whichis provided at the top with a control damper 14. From here the coolingair passes through the space 16 between the intermediate casings 15 and19 and downwards to cooling pipes 17 which conduct the air through thefluidised bed 9 and opens out into the space 11 between the combustionchamber 6 and the intermediate casing 19. Here the cooling air is mixedwith the flue-gas which emanates from the separators l and the entireamount of air passes through the pipe 12 to the turbine 20.

As mentioned earlier, it is most important that the amounts of coolingair and combustion air have a constant proportion relative to eachother, which can be achieved by means of an exact, relative adjustmentof the regulating dampers and 14. If, the efficiency of the combustionchamber and consequently that of the turbine, should thereafter bevaried by adjusting the regulating valve 2, said proportion between theamounts of air will remain substantially constant as will also thetemperature of the combustion chamber.

The supply of fuel to the fluidised bed through the pipe 7 must becarefully regulated to follow the regulation of the air, which has beenindicated purely symbolically in the FIGURE by connecting the fuel valve21 in the pipe 7 to the air valve 2 in the pipe 1.

A certain, minor variation of the above-mentioned proportions in theamounts of air under varying load conditions is conceivable which can bedone by finely adjusting one of the dampers 5 or 14 in relation to theadjustment of the air valve 2.

It has been found that a combustion chamber temperature of about 850 anda proportion of 1:2 between the amounts of combustion air and coolingair constitute a suitable adjustment combination.

Also shown on the drawing is a by-pass tube 25 having a valve 26 whichconnects the outer casing 4 with the outlet pipe 12. In this manner itis possible, in the event of an emergency stop or a sudden stop, toshortcircuit the fluidised bed itself as well as to supply cold air tothe turbine 20 by opening the valve 26, thus rap idly decreasing thepower output of the turbine especially if it operates its owncompressor. Simultaneously the valves 2 and 21 are throttled.

In the above-mentioned description it has been assumed that cooling airand combustion air emanate both from the same source and proceed to thesame consumer, but it is also conceivable to keep the air streamsseparated, either only at the outlet side or at both the inlet andoutlet sides.

For this purpose there may be an additional intermediate casing 22(dashed line) surrounding the outlets from the tubes 17 and from wherethe purged, hot cooling air is passed through a pipe 23 to a turbine(not shown) which will thus operate with purged, hot air. The coolingair may be taken from a separate air source through an intake 24 (dashedline), in which case the outer casing 4 becomes substantiallyunnecessary.

In this manner, the cooling system is capable of working at another,preferably higher, pressure than the combustion chamber, but still theproportional relationship between the two volumes of air is maintained.However, this arrangement makes the control somewhat more complicated.

It is also conceivable to interconnect the regulating valves for thefuel and the two air streams. Another possibility is to control thestream of cooling air in relation to the combustion chamber temperatureso that the latter is kept constant, which essentially also means aconstant proportional relationship between the volumes of air.

By reason of the separate cooling air system according to the inventionother gases than atmospheric air may be used for cooling; even and alsowater vapour is conceivable. The combustion chamber then acquires thecharacter of a superheater for a steam system, for example a steamturbine.

I claim:

1. A combustion chamber for operating gas turbines and the like;comprising:

a. a burner housing;

b. a fluidized bed of particulate material within said burner housing;

c. means for purging the combustion gas from said burner housing;

d. a chamber surrounding said burner housing for receiving purgedcombustion gas from said burner;

e. means for injecting fuel into said burner;

f. means for introducing combustion air into said burner;

g. a cooling chamber for receiving a cooling medium surrounding thepurged combustion gas chamber;

h. means for introducing a cooling medium into said cooling chamber;

i. means for passing said cooling medium in a confined path through saidfluidized bed in heat relationship therewith;

j. means for passing said cooling medium and said purged combustion gasto a power out-put station, and

k. means for maintaining a predetermined proportional relationshipbetween combustion air and said cooling medium constant regardless ofvarying power out-put demands and to maintain the fluidized bedtemperature within a predetermined range.

2. A combustion chamber according to claim I, having second controlmeans for simultaneous regulation of the volumes of combustion air andcooling medium on the one hand and the amount of fuel on the other.

3. A combustion chamber according to claim 1, in which the volume ofcombustion air and cooling medium are controlled to maintain acombustion temperature ranging between 700950C.

4. A combustion chamber according to claim 1, in which the volumes ofcombustion air and cooling medium are controlled to maintain aproportional relationship on the order of 1:2.

5. A combustion chamber according to claim 1, in which the coolingmedium constitutes air emanating from the same source as the combustionair.

6. A combustion chamber according to claim 5, in which a portion of theair emanating from the same sources is introduced into the coolingchamber as cooling medium and another portion thereof is introduced intothe fluidized bed as combustion air; the cooling air upon having passedthrough the fluidized bed being received in said purged combustion gaschamber and housing for short-circuiting the fluidized bed and passingthe air in the outer housing directly to the power out-put station forrapid reduction of the power out-put thereof.

9. A combustion chamber according to claim 1, in which a separate casingis provided surrounding said burner housing for confining the heatedcooling medium and having means for passing it separately to a differentpower out-put station.

1. A combustion chamber for operating gas turbines and the like;comprising: a. a burner housing; b. a fluidized bed of particulatematerial within said burner housing; c. means for purging the combustiongas from said burner housing; d. a chamber surrounding said burnerhousing for receiving purged combustion gas from said burner; e. meansfor injecting fuel into said burner; f. means for introducing combustionair into said burner; g. a cooling chamber for receiving a coolingmedium surrounding the purged combustion gas chamber; h. means forintroducing a cooling medium into said cooling chamber; i. means forpassing said cooling medium in a confined path through said fluidizedbed in heat relationship therewith; j. means for passing said coolingmedium and said purged combustion gas to a power out-put station, and k.means for maintaining a predetermined proportional relationship betweencombustion air and said cooling medium constant regardless of varyingpower out-put demands and to maintain the fluidized bed temperaturewithin a predetermined range.
 2. A combustion chamber according to claim1, having second control means for simultaneous regulation of thevolumes of combustion air and cooling medium on the one hand and theamount of fuel on the other.
 3. A combustion chamber according to claim1, in which the volume of combustion air and cooling medium arecontrolled to maintain a combustion temperature ranging between700*-950*C.
 4. A combustion chamber according to claim 1, in which thevolumes of combustion air and cooling medium are controlled to maintaina proportional relationship on the order of 1:2.
 5. A combustion chamberaccording to claim 1, in which the cooling medium constitutes airemanating from the same source as the combustion air.
 6. A combustionchamber according to claim 5, in which a portion of the air emanatingfrom the same sources is introduced into the cooling chamber as coolingmedium and another portion thereof is introduced into the fluidized bedas combustion air; the cooling air upon having passed through thefluidized bed being received in said purged combustion gas chamber andmixed therein with the combustion gas and passed as a combined entity tothe power out-put station.
 7. A combustion chamber according to claim 6which is provided with an outer housing surrounding said cooling chamberforming a passage for the air emanating from the common source which isintroduced into the fluidized bed and into the cooling chamberrespectively at a predetermined controlled rate.
 8. A combustion chamberaccording to claim 7, in which a valved by-pass passage is provided insaid outer housing for short-circuiting the fluidized bed and passingthe air in the outer housing directly to the power out-put station forrapid reduction of the power out-put thereof.
 9. A combustion chamberaccording to claim 1, in which a separate casing is provided surroundingsaid burner housing for confining the heated cooling medium and havingmeans for passing it separately to a different power out-put station.